Annealing furnace



Nov. 28, 1939. A, N. oTls 1 ANNEALING FURNAGE Filed April 50, 1958 Inventor: Albert N. Ov by w is, J

H iS Attorney.

Patented Nov. 28, 1939 ANNEALING FURNACE Albert N. om, Schenectady, N. Y., mignon-,so

General Electric Company, a corporation of New York Application April 30, 1938, Serial No. 205,292

4 Claims'.

My invention relates to annealing furnaces of the type adapted forl the continuous' annealing of strip material, such as steel strip, particularly where the surface of the strip to be annealed is bright or highly polished and must not be oxidized or scratched in the process. An example of a furnace of that type is disclosed in the joint patent to James L. McFarland and myself, 2,009,856. It is well known to those skilled in the art that with such a furnace a given heat treatment of a strip of given width and thickness depends upon various factors such as the temperature in the furnace, the speed of the moving strip, the rate at which the strip is heated and subsequently cooled, etc. For a particular heat treatment of a particular strip there is accordingly an upper limit to the length of the strip, hence the tonnage thereof, which can be treated in the furnace per hour. A greater tonnage output obviously may be obtained by increasing the height of the furnace and accordingly increasing the rate of travel of the strip therethrough but since a furnace of the type illustrated in that patent and suitable for the treatment of commercial steel strip already is of large proportions any material'increase in its height involves various diiilculties which are not easy to overcome. Among such diiliculties are the tendency of materials ordinarily used in the construction of furnace walls to crush' due to the superimposed weight and the tendency of the strip in the high temperature portion of the furnace to stretch or break due to itsxown weight and to the necessary tension applied thereto for its movement.

In accordance with my invention, I have provided a modified arrangement of furnace of this character whereby the capacity of the furnace is greatly increased, in fact doubled, without increasing the height of the furnace, the temperature therein, or the rate of travel of the strip. I provide my improved furnace with two separate and independent strip supporting rolls having the form of cantilevers each being supported in bearings outside of the furnace walls but having their free ends adjacent each other and each adapted to support a separate strip. Thus I am able to heat treat duplicate strips simultaneously in the same furnace.

Another important advantage of the construction which I have devised is that it enables me to heat treat in one furnace simultaneously two strips which differ in width' or in thickness or in both. Moreover, by separately controlling the movements of the two strips I can give the one strip a different heat treatment from that given to the other. Furthermore should trouble develop anywhere along one strip, the driving mechanism therefor may be shut down without necessitating any interruption in the treatment of the other strip.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a verticalA cross sectional view of an embodiment of my invention; Fig. 2 is a similar Viewv taken at right angles to that of Fig. l, and Fig. 3 is a circuit diagram of the control apparatus therefor. In the drawing, I is the outer steel shell of the furnace which is supported in an elevated position by the legs 2. The top of the shell I is covered by the cap 3 to facilitate accessibility to the strip supporting rolls. Within the shell and the cover is a layer l of heat insulating material which has a lining 5 of a suitable refractory material. Extending across the upper portion of the furnace is the partition 1 forming the upper chamber 8 in which are housed the strip supporting rolls. In the chamber beneath the partition 'I is the Ivertical partition I0 thereby forming the two heating chambers II and I2, on the walls of which are mounted the electric heating units I3 by which the ytemperature in each chamber is maintained at the desired value. For example, chamber II for a certain character of annealing may be kept at a temperature of 1300 F. and the temperature in the other chamber I2 may be kept at 1800 F., it being understood that the strip progresses from the chamber II to the chamber I2. In the lower portion of the partition I0, I have shown the opening I4 controlled by the damper I5 by which the protective atmosphere admitted to the furnace by the pipe I6' may circulate from the chamber I I to the chamber I2. v

Arranged in the upper chamber 8 are the two cantilever rolls I8 each of which supports a separate strip I9 of the material being annealed in the furnace. Since the strip must conform to the curvature of the roll by which it is supported, the diameter of the roll or at least that part of it contacting with the strip is relatively large. The rest of the roll preferably has a smaller diameter particularly the part which passes through and projects beyond the furnace wall. Each roll is supported by the spaced bearings 20 which are mounted on the bracket 2 I, a suitable stuffing box 22 being provided where the roll passes through the outer shell 4. For driving each cantilever rol,

particularly when starting the movement of a strip through the furnace; I provide the motor 23 mounted on the same bracket 2I and I connect its shaft by worm gearing to the roll. As I may prefer to use this motor for starting purposes only, the worm gear 24 of the worm gearing connects with the roll through an over-running clutch'which conveniently may be mounted within the worm gear. Each of the two strips being annealed in the furnace is suspended from one of the rolls I 8, the strips passing through suitable openings 25 iny the partition 1 and also through similar openings 26 in the bottom of the furnace.

Inthe housing 21 of the furnace are two pairs of cantilever rolls 28 and 29 which are supported by the bearings 30 and by which the strips are guided .to and from. the heating chambers. I have shown the rolls 28 and 29 as idlers but in certain'cases, I may prefer to drive them from motors supplied from the generators 46 and 41. By means ofthe pinch rolls 32 driven by the motor 33, each strip is drawn from the previous apparatus or from a reel and fed to the roll 29, a suitable seal 34 being provided at the entrance to the casing 21. The strip is drawn from the furnace by the pinch rolls 36 driven by the motor 31. Between the roll 29 and the pinch rolls 36, I have shown the cooling chamber 38 which may, if desired, be provided with a water jacket, a suitable seal 39 being provided where the strip leaves the cooling chamber. Within the cooling chamber, the strip is supported on the rolls 46 which preferably are .driven by motors, not shown, from the generators 46 and 41 to avoid any possibility of a highly polished strip being scratched thereby.

In the control circuit diagram illustrated by Fig. 3, the three-phase motor 45 drives the two direct current generators 46 and 41 of which the former supplies energy for moving one strip and the latter energy for independently moving the other strip. Each generator has a separately excited eld winding being supplied by direct i current from the source 48 through separate l rheostats 49 and 50. The armature circuits of the motors 33, 23 and 31 which move one strip are supplied in parallel from the generator 41 but the field windings of those motors are supplied from the source 48. In circuit with each eld winding is the rheostat and since it is desirable that the motors which move each strip shall operate in unison the three rheostats are coupled for unitary control asindicated by the dot and dash line. During the normal operation of the apparatus, I prefer that the motor 31 be arrangedv so that vit tends to operate at a somewhat higher speed than either of the other two motors, hence, I have provided the additional rheostat 52 in its i'leld circuit and the rheostat 53 in its armature circuit, so that its torque may be regulated to maintain some tension in the strip.

For driving the other strip, I employ similar motors 33', 23' and 31 whose armature circuits l are supplied from the generator 46 and whose eld windings are supplied from the same source 48, the control apparatus being like that for the corresponding motors 33, 23 and 31 respectively.

With the above described furnace structure and control apparatus, it will be seen that two separate. strips may be annealed simultaneously but independently in the same furnace, giving a large output in a furnace of moderate height. The two strips may be identical in form and character and be given the same heat treatment or the one may be given different heat treatment from the other by moving it at a different speed' through the furnace. On the other hand, the two strips may differ in width, thickness or character and yet be given the same treatment or they may be given diiferent treatment. Moreover the movement of one strip may be stopped entirely without interfering with the treatment of the other strip. A l

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A continuous strip annealing furnace havv ing a heating chamber and constructed and arranged simultaneously to anneal a plurality of separate strips comprising an upright structure, heating means therein, a plurality of axially alined cantilever rolls in said structure having their freelends adjacent and each arranged to support one of said strips independently of the other, bearings for said rolls supported by the walls of the structure, separatev driving means for moving each of said strips and separate speed controlling means for each of said driving means, whereby two like strips may' be given different heat treatment simultaneously in the vsame heating chamber or two strips havingdiiferent physical characteristics may be given like heat treatment simultaneously in the same heating chamber.

2. A continuous strip annealing furnace constructed and arranged simultaneously to anneal a plurality of separate strips of different\widths and thicknesses and requiring different heat treatment, comprising van upright structure, electric heating means on the walls thereof, a plurality of opposed cantilever rolls in the upper portion of said furnace arranged for separately and independently supporting said strips at the adjacent ends of the rolls, a plurality of bearings for each of said rolls supported externally of the furnace wall, separate motor means for driving each strip and means for independently controlling each motor means.

3. A continuous strip annealing furnaceconstructed and arranged to anneal a plurality of separate strips simultaneously comprising an upright structure having a central partition forniing two heating chambers and a transverse partition adjacent the upper end thereof forming a roll chamber, a pair of opposed cantilever'rolls in said roll chamber for supporting therefrom a portion of each strip in each of said heating chambers and having reduced portions extending outwardly through the opposite walls of the structure, a plurality of spaced bearings for said rolls supported exteriorly of said walls, a separate motor geared to-drive each roll, a plurality of pairs of cantilever rolls below said structure for guiding the strips thereto and therefrom and means for moving the strips to and from said guiding rolls.

4. A continuous strip annealing furnace constructed and arranged to anneal a plurality of separate strips simultaneously comprising an upright structure having heating means therein and havingv a plurality of vertical chambers, a

pair of strip suspending, opposed cantilever rolls depending portions thereof, means for feeding the strips to one of said pairs of guide rolls and means for withdrawing the strips from the other of said pair of guide rolls. ALBERT N. OTIS. 

